1. Field of the Invention
The present invention relates to a coupling mechanism, more specifically, to a spinning-reel spool coupling structure for coupling a spinning-reel spool to a spool shaft in a non-rotatable state while the spool shaft passes through the spinning-reel spool.
2. Background Information
In well-known spinning-reel spool coupling structures, a spool is coupled to a spool shaft in a unitarily rotatable state (i.e., a non-rotatable state or the spool does not rotate relative to the spool shaft) while being attached to and prevented from rotating at the distal end of the spool shaft. In some of the lever-brake spinning reels and the rear-drag spinning reels, for instance, the spool is coupled to the distal end of the spool shaft while being prevented from rotating with respect to the spool shaft. Japan Examined Utility Model Application Publication No. JP-Y-2603123 (especially, FIG. 10 thereof) describes a spinning reel with this type of structure.
In the well-known spool coupling structures, the spool is prevented from rotating about the spool shaft by detachably inserting an anti-rotation pin into a through hole radially passing through the spool shaft. More specifically, the spool is prevented from rotating about the spool shaft with a structure such that the outer peripheral surface of the anti-rotation pin is fitted with an anti-rotation groove formed on a boss portion of the spool along the diameter of the boss portion. Note the boss portion herein allows the spool shaft to pass through. The anti-rotation pin includes a flanged portion with a large diameter on a longitudinal intermediate part of its outer periphery in order to prevent detachment from the anti-rotation groove. The anti-rotation pin is further provided with an O-ring attached thereto for preventing detachment from the anti-rotation groove. Specifically, the attachment position of the O-ring is opposite to the position of the flanged portion through the spool shaft. In this position, the O-ring is allowed approximately to make contact with the spool shaft. More specifically, the O-ring is attached to an annular groove formed on the outer peripheral surface of the anti-rotation pin for preventing its axial movement. The annular groove can be positioned closer to the outer peripheral surface of the spool shaft.
Large tension generally acts on a fishing line when a fish is caught. Accordingly, a large force acts on the spool in its rotational direction. When the spool shaft is not smoothly rotated in addition to the condition, a large shear force acts on a boundary of the anti-rotation pin adjoining the spool shaft in the aforementioned spool coupling structure. In the lever-brake spinning reels configured to brake the rotor, for instance, a large shear force acts on the anti-rotation pin when a large tension acts on the fishing line and the rotor is herein braked. In the rear-drag spinning reels, on the other hand, large shear force acts on the anti-rotation pin when large tension acts on the fishing line under the condition that smooth rotation of the spool shaft is prevented by increasing drag force.
Incidentally, reduction in the diameter of the spool shaft has been demanded to reduce the entire size of the spinning reels. When the diameter of the spool shaft is reduced, sufficient strength cannot be ensured for the spool shaft unless the diameter of the anti-rotation pin is also reduced. This is because a ratio of the inner diameter of the through hole with respect to the outer diameter of the spool shaft is increased and thickness of the spool shaft is reduced in a surrounding area of the through hole. Therefore, reduction in diameter of the anti-rotation pin is required in response to that of the spool shaft. When a shear force acts on the outer peripheral surface of the spool shaft, however, stress concentrates on the annular groove and its periphery in the anti-rotation pin with a reduced diameter. It is therefore difficult to ensure sufficient strength for the anti-rotation pin.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved spinning-reel spool coupling structure for ensuring strength of an anti-rotation pin even when the diameter of the anti-rotation pin is reduced in response to reduction in diameter of the spool shaft. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.